U.S. patent application number 13/045656 was filed with the patent office on 2011-11-17 for motor driving circuit.
This patent application is currently assigned to ROHM CO., LTD.. Invention is credited to Tatsuro SHIMIZU.
Application Number | 20110282605 13/045656 |
Document ID | / |
Family ID | 44797903 |
Filed Date | 2011-11-17 |
United States Patent
Application |
20110282605 |
Kind Code |
A1 |
SHIMIZU; Tatsuro |
November 17, 2011 |
MOTOR DRIVING CIRCUIT
Abstract
A test signal generating circuit generates an AC test signal. A
driving unit supplies, to a motor, a driving voltage on which the
test signal has been superimposed. A current detection circuit
generates a detection signal that corresponds to an actual current
that flows through a coil of the motor. A filter extracts, from the
detection signal, a frequency component that corresponds to the
test signal. A coil constant calculation circuit calculates the
resistance value and the inductance value of the motor based upon
the amplitude of the detection signal output from the filter, the
amplitude of the test signal, and the phase difference between
these signals.
Inventors: |
SHIMIZU; Tatsuro; (Ukyo-Ku,
JP) |
Assignee: |
ROHM CO., LTD.
Kyoto
JP
|
Family ID: |
44797903 |
Appl. No.: |
13/045656 |
Filed: |
March 11, 2011 |
Current U.S.
Class: |
702/65 |
Current CPC
Class: |
H02P 7/29 20130101 |
Class at
Publication: |
702/65 |
International
Class: |
G06F 19/00 20110101
G06F019/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 12, 2010 |
JP |
JP2010-055335 |
Claims
1. A driving circuit configured to drive a motor having a
resistance and an inductance, the driving circuit comprising: a
test signal generating circuit configured to generate an AC test
signal; a driving unit configured to supply, to the motor, a
driving signal on which the test signal has been superimposed; a
current detection circuit configured to generate a detection signal
that corresponds to an actual current that flows through a coil
included in the motor; a filter configured to extract a frequency
component that corresponds to the test signal from the detection
signal; and a coil constant calculation circuit configured to
calculate the resistance value and the inductance value of the
motor based upon the amplitude of a detection signal output from
the filter, the amplitude of the test signal, and the phase
difference between these two signals.
2. A driving circuit according to claim 1, wherein the test signal
generating circuit is configured to adjust the frequency of the
test signal such that the phase difference between the test signal
and the detection signal output from the filter becomes a
predetermined target value.
3. A driving circuit according to claim 2, wherein the target value
is substantially 45 degrees.
4. A driving circuit according to claim 2, wherein the coil
constant calculation circuit comprises a resistance estimator
configured to calculate the resistance value of the motor by
multiplying a value, which is obtained by dividing the amplitude of
the test signal by the amplitude of the detection signal output
from the filter, by a predetermined coefficient that corresponds to
the target value.
5. A driving circuit according to claim 4, wherein the resistance
estimator comprises: memory configured to store a calculated
resistance value; a first calculation unit configured to multiply
the resistance value stored in the memory by the amplitude of the
detection signal output from the filter; a second calculation unit
configured to calculate the difference between the output data of
the first calculation unit and a value obtained by multiplying the
amplitude of the test signal by a predetermined coefficient; a
third calculation unit configured to convert the output data of the
second calculation unit into multi-valued data; and a fourth
calculation unit configured to generate the sum of the resistance
value stored in the memory and the output data of the third
calculation unit, and to store the value thus obtained in the
memory, thereby updating the resistance value.
6. A driving circuit according to claim 2, wherein the coil
constant calculation circuit comprises an inductance estimator
configured to calculate the inductance value of the motor by
dividing the resistance value thus calculated by a value that
corresponds to the frequency of the test signal.
7. A driving circuit according to claim 6, wherein the inductance
estimator comprises: memory configured to store a calculated
inductance value; a fifth calculation unit configured to multiply
the inductance value stored in the memory by the resistance value;
a sixth calculation unit configured to calculate the difference
between the data that represents the frequency of the test signal
and the output data of the fifth calculation unit; a seventh
calculation unit configured to convert the output data of the sixth
calculation unit into multi-valued data; and an eighth calculation
unit configured to generate the sum of the inductance value stored
in the memory and the output data of the seventh calculation unit,
and to store the value thus obtained in the memory, thereby
updating the inductance value.
8. A driving circuit according to claim 2, wherein the test signal
generating circuit comprises: a counter configured to generate
count data having a sawtooth waveform having a period that
corresponds to the frequency of the test signal; a CORDIC
(COordinate Rotation DIgital Computer) configured to receive the
count data from the counter, and to convert the count data thus
received into a trigonometric function value; and an up/down
counter configured to receive a first signal, which is obtained by
converting, into binary data, data that is obtained by shifting the
count data by an amount that corresponds to the target value, and a
second signal, which represents the sign of the detection signal
output from the filter, and to perform a counting up operation
according to one of the data thus received, and to perform a
counting down operation according to the other data thus received,
and wherein the counter controls the period of the count data based
upon the output data of the up/down counter.
9. A driving circuit according to claim 1, further comprising a
back electromotive force estimation circuit configured to generate
a back electromotive force estimation signal that represents an
estimated value of the back electromotive force that occurs in the
coil, based upon a driving signal that corresponds to the driving
voltage and the detection signal, wherein, with the sampling period
as dT, and with the resistance of the motor as R and the inductance
of the motor as L, the back electromotive force estimation circuit
comprises: a ninth calculation unit configured to calculate the
difference between the driving signal and the back electromotive
force estimation signal; a tenth calculation unit configured to
multiply the output data of the ninth calculation unit by dT/L; a
current estimation circuit configured to estimate a current that
flows through the coil, based upon the output data of the tenth
calculation unit, comprising an eleventh calculation unit
configured to multiply the estimated current value by
(1-dT/L.times.R), a twelfth calculation unit configured to generate
the sum of the output data of the tenth calculation unit and the
output data of the eleventh calculation unit, and a delay circuit
configured to delay the output data of the twelfth calculation unit
by a period dT and to output the current value thus estimated as
output data; and a back electromotive force calculation unit
configured to generate the back electromotive force estimation
signal such that the difference between the actual current value
represented by the detection signal and the current value thus
estimated becomes zero.
10. A driving circuit according to claim 9, wherein the driving
unit adjusts the phase of the driving voltage such that the timing
of the zero-crossing point of a waveform represented by the back
electromotive force estimation signal matches the timing of the
zero-crossing point of the current represented by the detection
signal.
11. A cooling apparatus comprising: a fan motor having a resistance
and an inductance; and a driving circuit configured to drive the
fan motor, the driving circuit comprising: a test signal generating
circuit configured to generate an AC test signal; a driving unit
configured to supply, to the motor, a driving signal on which the
test signal has been superimposed; a current detection circuit
configured to generate a detection signal that corresponds to an
actual current that flows through a coil included in the motor; a
filter configured to extract a frequency component that corresponds
to the test signal from the detection signal; and a coil constant
calculation circuit configured to calculate the resistance value
and the inductance value of the motor based upon the amplitude of a
detection signal output from the filter, the amplitude of the test
signal, and the phase difference between these two signals.
12. An electronic device comprising: a processor; and a cooling
apparatus configured to cool the processor, the cooling apparatus
comprising: a fan motor having a resistance and an inductance; and
a driving circuit configured to drive the fan motor, wherein the
driving circuit comprises: a test signal generating circuit
configured to generate an AC test signal; a driving unit configured
to supply, to the motor, a driving signal on which the test signal
has been superimposed; a current detection circuit configured to
generate a detection signal that corresponds to an actual current
that flows through a coil included in the motor; a filter
configured to extract a frequency component that corresponds to the
test signal from the detection signal; and a coil constant
calculation circuit configured to calculate the resistance value
and the inductance value of the motor based upon the amplitude of a
detection signal output from the filter, the amplitude of the test
signal, and the phase difference between these two signals.
13. A method for estimating the resistance and the inductance of a
motor, the method comprising: superimposing an AC test signal on a
driving voltage to be applied to the motor; generating a detection
signal that corresponds to an actual current that flows through a
coil included in the motor; extracting a frequency component that
corresponds to the test signal from the detection signal; and
calculating the resistance value and the inductance value of the
motor based upon at least one of the amplitude of the extracted
detection signal, the amplitude of the test signal, and the phase
difference between these two signals.
14. A method according to claim 13, further comprising adjusting
the frequency of the test signal such that the phase difference
between the extracted detection signal and the test signal becomes
a predetermined target value.
15. A method according to claim 14, wherein the target value is
substantially 45 degrees.
16. A method according to claim 14, further comprising: calculating
the resistance value of the motor by multiplying a value, which is
obtained by dividing the amplitude of the test signal by the
amplitude of the detection signal thus extracted, by a
predetermined coefficient; and calculating the inductance value of
the motor by dividing the resistance value thus calculated by a
value that corresponds to the frequency of the test signal.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a sensorless motor driving
technique.
[0003] 2. Description of the Related Art
[0004] There are two known methods for driving a DC motor or a
spindle motor, i.e., a method using a Hall sensor or a velocity
sensor, and a sensorless driving method using back electromotive
force that occurs in a coil of a motor without involving a sensor.
With a method using such a sensor, it is difficult to suppress the
effects of irregularities in such sensors.
[0005] In contrast, with such a sensorless driving method, assuming
that the resistance and the inductance of the coil are known, the
back electromotive force is estimated, and the estimated value of
the back electromotive force is used in the driving operation for
the motor. With typical arrangements, after the resistance value
and the inductance value of the coil are measured, the same values
are used continuously.
RELATED ART DOCUMENTS
Patent Documents
[Patent Document 1]
[0006] Japanese Patent Application Laid Open No. 2005-224100
[Patent Document 2]
Japanese Patent Application Laid Open No. 2000-166285
[0007] It is known that the resistance and the inductance of a
motor are each subject to the effects of temperature. In
particular, with a fan motor configured to cool a CPU (Central
Processing Unit) or the like, the temperature of the coil changes
in a wide range. This leads to large fluctuation in the resistance
and the inductance, resulting in it becoming difficult to precisely
estimate the back electromotive force. If the back electromotive
force cannot be estimated with sufficient precision, such an
arrangement has a problem of large vibration or large noise of the
motor, or otherwise a problem of large power consumption. Such
problems do not occur only in such a fan motor, but also occur in a
driving operation for driving any other kind of motor using a
sensorless method.
SUMMARY OF THE INVENTION
[0008] The present invention has been made in view of such a
situation. Accordingly, it is an exemplary purpose of the present
invention to provide a motor driving method for measuring the
resistance and the inductance of a motor so as to estimate the back
electromotive force thereof with high precision.
[0009] An embodiment of the present invention relates to a driving
circuit configured to drive a motor having a resistance and an
inductance. The driving circuit comprises: a test signal generating
circuit configured to generate an AC test signal; a driving unit
configured to supply, to the motor, a driving signal on which the
test signal has been superimposed; a current detection circuit
configured to generate a detection signal that corresponds to an
actual current that flows through a coil; a filter configured to
extract a frequency component that corresponds to the test signal
from the detection signal; and a coil constant calculation circuit
configured to calculate the resistance value and the inductance
value of the motor based upon the amplitude of a detection signal
output from the filter, the amplitude of the test signal, and the
phase difference between these two signals.
[0010] With such an embodiment, the inductance and the resistance
of the motor can be measured while the motor is being driven.
[0011] Also, the test signal generating circuit may be configured
to adjust the frequency of the test signal such that the phase
difference between the test signal and the detection signal output
from the filter becomes a predetermined target value. Also, the
target value may be substantially 45 degrees.
[0012] In such an arrangement, on the assumption that the phase
difference matches the target value, the resistance value and the
inductance value can be calculated by the coil constant calculation
circuit. Thus, such an arrangement provides a simplified
calculation operation.
[0013] Also, the coil constant calculation circuit may comprise a
resistance estimator configured to calculate the resistance value
of the motor by multiplying a value, which is obtained by dividing
the amplitude of the test signal by the amplitude of the detection
signal output from the filter, by a predetermined coefficient that
corresponds to the target value.
[0014] Also, the resistance estimator may comprise: a first
calculation unit configured to multiply the calculated resistance
value by the amplitude of the detection signal output from the
filter; a second calculation unit configured to calculate the
difference between the output data of the first calculation unit
and a value obtained by multiplying the amplitude of the test
signal by a predetermined coefficient; a third calculation unit
configured to convert the output data of the second calculation
unit into multi-valued data; and a fourth calculation unit
configured to generate the sum of data that represents the latest
calculated resistance value and the output data of the third
calculation unit so as to update the resistance value.
[0015] Also, the coil constant calculation circuit may comprise an
inductance estimator configured to calculate the inductance value
of the motor by dividing the resistance value thus calculated by a
value that corresponds to the frequency of the test signal.
[0016] Also, the test signal generating circuit may comprise: a
counter configured to generate count data having a sawtooth
waveform having a period that corresponds to the frequency of the
test signal; a CORDIC (COordinate Rotation DIgital Computer)
configured to receive the count data from the counter, and to
convert the count data thus received into a trigonometric function
value; and an up/down counter configured to receive a first signal,
which is obtained by converting, into binary data, data that is
obtained by shifting the count data by an amount that corresponds
to the target value, and a second signal, which represents the sign
of the detection signal output from the filter, and to perform a
counting up operation according to one of the data thus received,
and to perform a counting down operation according to the other
data thus received. Also, the counter may control the period of the
count data based upon the output data of the up/down counter.
[0017] With such an embodiment, the up/down counter operates as a
phase comparator, which provides a feedback operation such that
phase difference between the test signal and the detection signal
matches the target value.
[0018] A driving circuit according to an embodiment may further
comprise a back electromotive force estimation circuit configured
to generate a back electromotive force estimation signal that
represents an estimated value of the back electromotive force that
occurs in the motor, based upon a driving signal that corresponds
to the driving voltage and the detection signal. Also, with the
sampling period as dT, and with the resistance of the motor as R
and the inductance of the motor as L, the back electromotive force
estimation circuit may comprise: a ninth calculation unit
configured to calculate the difference between the driving signal
and the back electromotive force estimation signal; a tenth
calculation unit configured to multiply the output data of the
ninth calculation unit by dT/L; a current estimation circuit
configured to estimate a current that flows through the coil, based
upon the output data of the tenth calculation unit; and a back
electromotive force calculation unit configured to generate the
back electromotive force estimation signal such that the difference
between the actual current value represented by the detection
signal and the current value thus estimated becomes zero.
[0019] Also, the current estimation circuit may comprise: an
eleventh calculation unit configured to multiply its estimated
current value by (1-dT/L.times.R); a twelfth calculation unit
configured to generate the sum of the output data of the tenth
calculation unit and the output data of the eleventh calculation
unit; and a delay circuit configured to delay the output data of
the twelfth calculation unit by a period dT and to output the
current value thus estimated as output data.
[0020] Also, the driving unit may adjust the phase of the driving
voltage such that the timing of the zero-crossing point of a
waveform of the estimated back electromotive force matches the
timing of the zero-crossing point of the current represented by the
detection signal.
[0021] Another embodiment of the present invention relates to a
method for estimating the resistance and the inductance of a motor.
The method comprises: superimposing an AC test signal on a driving
voltage to be applied to the motor; generating a detection signal
that corresponds to an actual current that flows through a coil
included; extracting a frequency component that corresponds to the
test signal from the detection signal; and calculating the
resistance value and the inductance value of the motor based upon
the ratio between the amplitude of the extracted detection signal
and the amplitude of the test signal.
[0022] It is to be noted that any arbitrary combination or
rearrangement of the above-described structural components and so
forth is effective as and encompassed by the present
embodiments.
[0023] Moreover, this summary of the invention does not necessarily
describe all necessary features so that the invention may also be a
sub-combination of these described features.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] Embodiments will now be described, by way of example only,
with reference to the accompanying drawings which are meant to be
exemplary, not limiting, and wherein like elements are numbered
alike in several Figures, in which:
[0025] FIG. 1 is a circuit diagram which shows a configuration of
an electronic device including a driving IC according to an
embodiment;
[0026] FIG. 2 is a circuit diagram which shows a configuration of a
back electromotive force estimation circuit;
[0027] FIG. 3A is a driving waveform diagram for a driving IC shown
in FIG. 1, and FIG. 3B is a driving waveform diagram for an
arrangement employing a Hall sensor;
[0028] FIG. 4 is a block diagram which shows a part of a
configuration of the driving IC;
[0029] FIG. 5 shows graphs each showing the frequency response
characteristics of the coil current with respect to the test signal
supplied to the fan motor;
[0030] FIG. 6 is a circuit diagram which shows a specific example
configuration of the driving IC shown in FIG. 4; and
[0031] FIGS. 7A through 7C are waveform diagrams each showing an
operating waveform for the test signal generating circuit shown in
FIG. 6.
DETAILED DESCRIPTION OF THE INVENTION
[0032] The invention will now be described based on preferred
embodiments which do not intend to limit the scope of the present
invention but exemplify the invention. All of the features and the
combinations thereof described in the embodiment are not
necessarily essential to the invention.
[0033] In the present specification, the state represented by the
phrase "the member A is connected to the member B" includes a state
in which the member A is indirectly connected to the member B via
another member that does not substantially affect the electric
connection therebetween, or that does not damage the functions or
effects of the connection therebetween, in addition to a state in
which the member A is physically and directly connected to the
member B.
[0034] An embodiment of the present invention relates to a motor
driving circuit configured to drive a DC motor. For example, such
an embodiment is preferably used in a driving operation for a fan
motor, a DC motor configured to drive a lens of a digital still
camera, a DC motor configured to drive a pickup head unit included
in an optical disk recording and playback apparatus for a CD
(Compact Disc), DVD (Digital Versatile Disc), or the like.
[0035] FIG. 1 is a circuit diagram which shows a configuration of
an electronic device 1 including a driving IC 100 according to an
embodiment. The electronic device 1 is configured as a desktop
computer, a laptop computer, a workstation, a game device, an audio
device, a video device, or the like, and includes a cooling
apparatus 2 and a CPU (Central Processing Unit) 4. The cooling
apparatus 2 includes a fan motor 6 arranged such that it faces the
CPU 4, and a driving IC 100 configured to drive the fan motor
6.
[0036] The fan motor 6 includes a coil. The equivalent circuit of
such a fan motor 6 is represented by a circuit comprising a
resistor R and an inductance L connected in series. The back
electromotive force Em(t) that occurs in the coil is represented by
a power supply.
[0037] The driving IC 100 is a function IC integrated on a single
semiconductor chip. The driving IC 100 estimates the back
electromotive force Em(t) that occurs in the fan motor 6, and
drives the fan motor 6 based upon the back electromotive force thus
estimated. FIG. 1 is a simplified schematic configuration of the
driving IC 100. It is needless to say that an arrangement may be
made having a configuration that is equivalent to, or that is
configured to perform an operation that is equivalent to, such an
arrangement shown in FIG. 1, which is encompassed in the technical
scope of the present invention.
[0038] The driving IC 100 includes a driving unit 10, a current
detection circuit 12, a back electromotive force estimation circuit
14, and a driving signal generating unit 16. The driving unit 10
applies a driving voltage V.sub.DRV(t) that corresponds to a
driving signal S.sub.DRV to the fan motor 6. The configuration of
the driving unit 10 is not restricted in particular. Rather,
various known techniques may be used to configure the driving unit
10. For example, with an arrangement configured to perform a BTL
driving operation, the driving voltage V.sub.DRV(t) is an analog
voltage which is continuous over time. On the other hand, with an
arrangement configured to perform a PWM driving operation, the
driving voltage V.sub.DRV(t) has a switching waveform.
[0039] The current detection circuit 12 generates a detection
signal S.sub.CS that corresponds to the driving current
i.sub.DRV(t) that flows through the coil of the fan motor 6. For
example, the current detection circuit 12 may include a detection
resistor R.sub.NF arranged on a path for the fan motor 6, and an
amplifier AMP1 configured to detect voltage drop that occurs
between both terminals of the detection resistor R.sub.NF. In a
case in which the driving unit 10 includes a bridge circuit or an
amplifier, the on-resistance of a transistor which is a component
of such a bridge circuit or an amplifier, and which is arranged on
a path for the driving current i.sub.DRV(t), may be used as the
detection resistor R.sub.NF.
[0040] The back electromotive force estimation circuit 14 estimates
the back electromotive force Em(t) that occurs at the coil based
upon the driving signal S.sub.DRV that represents the driving
voltage V.sub.DRV and a detection signal S.sub.IL. The back
electromotive force thus estimated and a signal that represents the
back electromotive force thus estimated will be represented by
Em.sub.hat(t).
[0041] The driving signal generating unit 16 generates a driving
signal S.sub.DRV based upon the driving signal S.sub.DRV (or
driving voltage V.sub.DRV) and the back electromotive force
estimation signal Em.sub.hat. The driving signal generating unit 16
adjusts the phase of the driving signal S.sub.DRV such that timing
of the zero-crossing point of the waveform of the back
electromotive force Em.sub.hat(t) thus estimated matches the timing
of the zero-crossing point of the coil current i.sub.DRV(t)
represented by the detection signal S.sub.CS. Thus, such an
arrangement provides minimized noise and vibration, and provides
reduced power consumption.
[0042] The driving signal generating unit 16 includes waveform
memory 20, a normalizing circuit 22, a PLL circuit 24, and a
calculation unit 26. The normalizing circuit 22 normalizes the back
electromotive force estimation signal Em.sub.hat, and writes the
back electromotive force estimation signal Em.sub.hat thus
estimated to the waveform memory 20. The waveform data thus written
to the waveform memory 20 is read out in synchronization with a
readout clock CLK output from the PLL circuit 24. The calculation
unit 26 multiplies the waveform data thus read out from the
waveform memory 20 by a torque setting value S.sub.TRQ so as to
generate the driving signal S.sub.DRV. The PLL circuit 24 adjusts
the frequency of the clock signal CLK such that the timing of the
zero-crossing point of the waveform of the back electromotive force
Em.sub.hat(t) thus estimated matches the timing of the
zero-crossing point of the coil current i.sub.DRV(t) represented by
the detection signal S.sub.CS.
[0043] The above is the overall configuration of the driving IC
100. Next, description will be made regarding the estimation of the
back electromotive force.
[0044] FIG. 2 is a circuit diagram which shows a configuration of
the back electromotive force estimation circuit 14. The back
electromotive force estimation circuit 14 includes a ninth
calculation unit 30, a tenth calculation unit 32, a current
estimation circuit 34, and a back electromotive force calculation
unit 42. As described above, the back electromotive force
estimation circuit 14 generates the back electromotive force
estimation signal Em.sub.hat which represents the estimated value
of the back electromotive force that occurs at the coil, based upon
the driving signal S.sub.DRV and the detection signal S.sub.CS.
[0045] The back electromotive force estimation circuit 14 is
configured as a digital circuit. The sampling period will be
represented by dT. Furthermore, the resistance value R and the
inductance value L of the fan motor 6 are taken to be known.
[0046] The ninth calculation unit 30 calculates the difference
between the driving signal S.sub.DRV and the back electromotive
force estimation signal Em.sub.hat. The tenth calculation unit 32
multiplies output data S30 of the ninth calculation unit 30 by a
coefficient (dT/L).
[0047] The current estimation circuit 34 estimates a current i(t)
that flows through the coil, based upon output data S32 of the
tenth calculation unit 32, and generates a current estimation
signal I.sub.hat which represents the current value thus estimated.
The current estimation circuit 34 includes an eleventh calculation
unit 36, a delay circuit 38, and a twelfth calculation unit 40. The
eleventh calculation unit 36 multiplies the current estimation
signal I.sub.hat by a coefficient (1-Td/L.times.R). The twelfth
calculation unit generates the sum of the output data of the tenth
calculation unit 32 and the output data of the eleventh calculation
unit 36. The delay circuit 38 delays the output data of the twelfth
calculation unit 40 by the delay time dT, so as to generate the
current estimation signal I.sub.hat.
[0048] The back electromotive force calculation unit 42 generates
the back electromotive force estimation signal Em.sub.hat such that
the difference between the actual current value I.sub.real
represented by the detection signal S.sub.CS and the current value
I.sub.hat thus estimated becomes zero. The back electromotive force
calculation unit 42 includes a thirteenth calculation unit 44, a
fourteenth calculation unit 46, a fifteenth calculation unit 48,
and a delay circuit 50.
[0049] The thirteenth calculation unit 44 calculates the difference
between the detection signal S.sub.CS and the current estimation
signal I.sub.hat. The fourteenth calculation unit 46 multiplies the
difference data S44 by a predetermined coefficient. The fifteenth
calculation unit 48 generates the sum of the back electromotive
force estimation signal Em.sub.hat and the output data S44 of the
thirteenth calculation unit 44. The delay circuit 50 delays the
output data S48 of the fifteenth calculation unit 48 by a delay
time unit period dT, and outputs the resulting signal as the
current estimation signal I.sub.hat.
[0050] The above is the configuration of the back electromotive
force estimation circuit 14. Next, description will be made
regarding its operating mechanism. When the driving voltage V(t) is
applied to the fan motor 6, the following relation expression holds
true.
V(t)=Em(t)+R i(t)+L d/dt i(t) (1)
[0051] The back electromotive force estimation circuit 14 is
configured to perform digital signal processing. Thus, Expression
(1) is transformed into a discrete-time system using the sampling
time dT, thereby obtaining the following Expression (2).
V.sub.n=Em.sub.n+R i.sub.n+L(i.sub.n+1-i.sub.n)/dT (2)
[0052] Expression (2) is solved for i.sub.n+1, thereby obtaining
the following Expression (3).
i.sub.n+1=(1-dT/L.times.R)i.sub.n+dT/L.times.(V.sub.n-Em.sub.n)
(3)
[0053] With the back electromotive force estimation circuit 14
shown in FIG. 2, the estimated value Em.sub.hat of the back
electromotive force is updated by a feedback operation such that
the estimated current value I.sub.hat matches the actual current
value I.sub.real. When these two current values match each other,
the feedback loop enters the steady state. In this state, the back
electromotive force estimation signal represents the actual back
electromotive force.
[0054] Thus, the back electromotive force estimation circuit 14
shown in FIG. 2 is capable of estimating the back electromotive
force that occurs at the fan motor 6.
[0055] FIG. 3A is a driving waveform diagram for the driving IC 100
shown in FIG. 1. FIG. 3B is a driving waveform diagram for an
arrangement employing a Hall sensor.
[0056] With an arrangement employing such a Hall sensor, the motor
driving phase is switched based upon a Hall signal received from
the Hall sensor. With such an arrangement, a large negative torque
component occurs at each phase switching timing as shown in FIG.
3B. This is because there is a phase difference between the Hall
signal and the back electromotive force that occurs in the motor.
Such a negative torque leads to deterioration in the driving
efficiency of the motor.
[0057] In contrast, with the driving IC 100 shown in FIG. 1, as
shown in FIG. 3A, the phase of the driving voltage is adjusted such
that the zero-crossing point of the driving current, i.e., the
zero-crossing point of the torque waveform of the motor, matches
the zero-crossing point of the back electromotive force. Thus, such
an arrangement suppresses the occurrence of such a negative torque,
thereby enabling the motor to be driven with high efficiency. The
driving method according to the embodiment has advantages of
improved noise and improved vibration in comparison with driving
methods employing a Hall sensor or a velocity sensor.
[0058] Assuming that the resistance R and the inductance L of the
fan motor 6 are each known, the back electromotive force estimation
circuit 14 shown in FIG. 2 is capable of estimating the back
electromotive force with high precision. However, the inductance L
and the resistance R of the motor fluctuate dynamically in the
driving operation of the motor. Accordingly, if the same resistance
value R and the same inductance value L are used continuously, such
an arrangement is not capable of estimating the back electromotive
force. In order to solve such a problem, description will be made
below regarding a technique for estimating the resistance R and the
inductance L of the motor with high precision.
[0059] FIG. 4 is a block diagram which shows a part of the
configuration of the driving IC 100. Of the configuration of the
driving IC 100, FIG. 4 shows only a block configured to provide a
function of estimating and calculating the constants R and L of the
fan motor 6, and the other blocks are not shown.
[0060] The driving IC 100 includes a driving unit 10, a current
detection circuit 12, a test signal generating circuit 60, a filter
64, and a coil constant calculation circuit 66.
[0061] The test signal generating circuit 60 generates an AC test
signal S.sub.TEST. For example, the test signal S.sub.TEST is
configured as a sine wave signal, and is represented by the
following Expression.
S.sub.TEST(t)=A sin(.omega..sub.0t)
[0062] A represents the amplitude of the test signal S.sub.TEST,
and .omega. represents the angular velocity (2.pi.f.sub.0). For
example, in a case in which the fan motor 6 is rotationally driven
in a range of 0 to 4000 rpm, the frequency of the motor is set to 0
to 70 Hz. The frequency of the test signal S.sub.TEST is set to a
value that is sufficiently higher than the frequency of the motor,
and is preferably set to a value that is ten times to fifty times
the frequency of the motor, for example. Specifically, the
frequency f.sub.0 of the test signal S.sub.TEST is set to 1
kHz.
[0063] The driving unit 10 corresponds to that shown in FIG. 1. The
driving unit 10 supplies, to the fan motor 6, a driving voltage
V.sub.DRV on which the test signal S.sub.TEST has been
superimposed. With an arrangement configured to perform a BTL
driving operation, the test signal S.sub.TEST is superimposed in
the amplitude direction of the driving signal V.sub.DRV. With an
arrangement configured to perform a PWM driving operation, the test
signal S.sub.TEST is superimposed in the pulse width direction of
the PWM pulse.
[0064] The current detection circuit 12 generates a detection
signal S.sub.CS that corresponds to the actual current i(t) that
flows through the coil of the fan motor 6. The filter 64 is a
bandpass filter configured to extract, from the detection signal
S.sub.CS, the frequency component that corresponds to the test
signal S.sub.TEST. The filter 64 is tuned so as to have a pass band
including the frequency f.sub.0. The output signal S.sub.CS' (which
will be referred to as the "detection signal" hereafter) of the
filter 64 is represented by the following Expression.
S.sub.CS'(t)=B sin(.omega..sub.0t+.theta.)
[0065] The coil constant calculation circuit 66 calculates the
resistance value R and the inductance value L of the fan motor 6
based upon the amplitudes A and B of the test signal S.sub.TEST and
the detection signal S.sub.CS' and the phase difference between
these signals.
[0066] The above is the basic configuration of the driving IC 100.
Next, description will be made regarding its operating
mechanism.
[0067] In general, if the motor is stationary, the resistance value
R can be calculated based upon the current that flows through the
coil when a voltage is applied to the coil. Furthermore, the
inductance value L can be calculated based upon the current
waveform obtained when a voltage is applied in a step response
manner. However, such a method cannot be used in the operation of
rotationally driving the motor.
[0068] The Laplace transform of Expression (1) is generated so as
to provide the transfer function for the current with respect to
the driving voltage.
I(s)/(V(s)-Em(s))=1/R.times.1/(1+L/R s) (4)
[0069] That is to say, it can be understood that the current
waveform I is represented by a waveform obtained by applying a
first-order low-pass filter to the voltage waveform, and the
amplitude thereof is represented by 1/R.
[0070] Now, the voltage V(t) represented by the following
Expression (5) is taken to be applied to the motor.
V(t)=Const+A sin(.omega.t) (5)
[0071] The back electromotive force provides a voltage that is
proportional to the rotational speed of the motor. Here, an AC
driving voltage V(t)=B sin(.omega..sub.0t) that is insufficient to
rotate the fan motor 6 is taken to be applied to the fan motor 6.
When the motor is not rotated, the driving voltage V(t) has no
effect on the back electromotive force. If there is a sufficiently
great difference between .omega. and the frequency of the control
voltage Const, the control voltage Const can be regarded as a DC
voltage. The transfer function configured to represent the relation
between the signal BPF_I(s) obtained by applying a bandpass filter
having a center frequency f=2.pi..omega. to the current I(s) and
the AC component V'(t)=A sin(.omega.t) is represented by a transfer
function of a first-order low-pass filter as represented in
Expression (4). This transfer function is dependent on neither the
back electromotive force Em nor the control voltage Const.
BPF.sub.--I(t)/V'(s)=1/R.times.1/(1+L/R s) (6)
[0072] FIG. 5 shows graphs each showing the frequency response
characteristics of the coil current with respect to the test signal
S.sub.TEST supplied to the fan motor 6. The upper graph shows the
gain characteristics thereof (i.e., the amplitude ratio between the
test signal and the output signal of the filter). The lower graph
shows the phase characteristics thereof.
[0073] The gain characteristics and the phase characteristics are
uniquely determined by the values of R and L. Thus, after the
amplitudes A and B of the test signal S.sub.TEST and the detection
signal S.sub.CS' and the phase difference .theta. between these
signals are acquired, the coil constant calculation circuit 66 is
capable of calculating the values of R and L with high precision
based upon the information thus acquired. The test signal
S.sub.TEST is configured as an AC signal, and has no effect on the
driving operation for the fan motor 6. Thus, such an arrangement is
capable of calculating the resistance value R and the inductance
value L of the fan motor 6 while the fan motor 6 is being driven.
Accordingly, such an arrangement is capable of detecting
fluctuation in the resistance R and the inductance L in the driving
operation even if the resistance R and the inductance L fluctuate.
Thus, such an arrangement is capable of estimating the back
electromotive force that occurs in the fan motor 6 with high
precision.
[0074] Acquisition of the respective amplitudes A and B of the test
signal S.sub.TEST and the detection signal S.sub.CS' and of the
phase difference .theta. between these signals leads to an increase
in the amount of calculation, which is troublesome. Description
will be made below regarding an operation for reducing the amount
of calculation.
[0075] With the present embodiment, the test signal generating
circuit 60 adjusts the frequency f.sub.0 of the test signal
S.sub.TEST such that the phase difference .theta. between the two
signals, i.e., the test signal S.sub.TEST and the detection signal
S.sub.CS' becomes a predetermined target value. With such a
technique, the coil constant calculation circuit 66 is capable of
calculating the resistance value R and the inductance value L on
the assumption that the phase difference .theta. between the
detection signal S.sub.CS' and the test signal S.sub.TEST matches
the target value, thereby providing a reduced amount of
calculation.
[0076] The test signal generating circuit 60 includes a frequency
adjustment unit 62. The frequency adjustment unit 62 controls the
frequency f0 of the test signal S.sub.TEST such that the phase
difference .theta. between the test signal S.sub.TEST and the
detection signal S.sub.CS' becomes the target value.
[0077] For example, the target value of the phase difference
.theta. is preferably set to 45.degree.. The frequency which
provides the phase difference .theta.=45.degree. matches the cutoff
frequency for a gain of -3 dB, and accordingly, the following
Expression holds true. Here, A is a known value, and B represents
the amplitude of the detection signal S.sub.CS'. Accordingly, the
resistance value R and the inductance value L can be calculated
based upon a simple calculation.
R=A/B.times.10.sup.-3/20=0.7.times.A/B [.OMEGA.]
L=R/.omega..sub.0 [H], which is obtained from
.omega..sub.0=1/(L/R)=R/L.
[0078] FIG. 6 is a circuit diagram which shows a specific example
configuration of the driving IC 100 shown in FIG. 4.
[0079] The coil constant calculation circuit 66 includes a
resistance estimator 68 and an inductance estimator 70. The
resistance estimator 68 calculates the resistance R of the fan
motor 6 by multiplying the value A/B, which is obtained by dividing
the amplitude A of the test signal S.sub.TEST by the amplitude B of
the extracted detection signal S.sub.CS', by a predetermined
coefficient .alpha.=0.7 that corresponds to the target value
(45.degree.).
[0080] The resistance estimator 68 includes memory units M1 through
M3, a first calculation unit 72, a second calculation unit 74, a
third calculation unit 76, and a fourth calculation unit 78. The
memory unit M1 stores a value obtained by multiplying the amplitude
A of the test signal S.sub.TEST by the coefficient 0.7. The second
memory unit M2 stores the peak value B of the detection signal
S.sub.CS'. The memory unit M3 stores the data D_1 which represents
the calculated resistance value R.
[0081] The first calculation unit 72 multiplies the value stored in
the memory unit M2 by the value D_1 stored in the memory unit M3.
The second calculation unit 74 subtracts the output data of the
first calculation unit 72 from the data 0.7 A stored in the memory
unit Ml. The third calculation unit 76 converts the output data of
the second calculation unit 74 into multi-valued data (e.g., binary
data). The fourth calculation unit 78 generates the sum of the
value stored in the memory unit M3 and the output data of the
second calculation unit 74, and stores the resulting data in the
memory unit M3 as the updated data D_1. By means of such an
operation, the value stored in the memory unit M3 represents the
resistance value R.
[0082] The inductance estimator 70 receives, as input data, the
data .omega. which represents the frequency of the test signal
S.sub.TEST. The inductance estimator 70 includes a memory unit M4,
a fifth calculation unit 80, a sixth calculation unit 82, a seventh
calculation unit 84, and an eighth calculation unit 86. The memory
unit M4 stores data D_2 which represents the calculated inductance
value L. The fifth calculation unit 80 multiplies the inductance
value L stored in the memory M4 by the resistance value R. The
sixth calculation unit 82 calculates the difference between the
data which represents the frequency .omega. of the test signal
S.sub.TEST and the output data of the fifth calculation unit 80.
The seventh calculation unit 84 converts the output data of the
sixth calculation unit 82 into multi-valued data. The eighth
calculation unit 86 generates the sum of the inductance value L
stored in the memory M4 and the output data of the seventh
calculation unit 84, and stores the resulting value in the memory
M4, thereby updating the inductance value L. By means of such an
operation, the value stored in the memory M4 represents the
inductance value L.
[0083] Next, description will be made regarding a configuration of
the test signal generating circuit 60. The test signal generating
circuit 60 includes a signal source 61 and a frequency adjustment
unit 62.
[0084] The signal source 61 includes a counter 90, a CORDIC 92, an
amplitude adjustment unit 94, a calculation unit 96, a calculation
unit 98, an up/down counter 99, and a compensator 93.
[0085] The counter 90 performs a counting up operation according to
the clock signal CLK so as to generate phase count data S90 having
a sawtooth waveform having a period T (=2.pi./.omega..sub.0) that
corresponds to the frequency .omega..sub.0 of the test signal
S.sub.TEST. The frequency .omega..sub.0 changes according to the
increment value .delta. in increments of cycles of the clock signal
CLK applied to the counter 90. The phase count data S90 is data
that corresponds to (.omega..sub.0t) in Expression (5).
[0086] The CORDIC 92 receives the phase count data S90 from the
counter 90, and converts the value of the phase count data S90 thus
received into a normalized trigonometric function value. The
amplitude adjustment unit 94 converts the amplitude of the output
data of the CORDIC 92 into the aforementioned value A.
[0087] The up/down counter 99 receives the data S1 that represents
the sign of the data, which is obtained by shifting the count data
S90 by a value that corresponds to the target phase value
45.degree., and receives the data that represents the sign of the
detection signal S.sub.CS' output from the filter 64. The up/down
counter 99 performs a counting up operation according to one of the
data thus received, and performs a counting down operation
according to the other data.
[0088] The count value S99 of the up/down counter 99 represents the
difference between a target value and the phase difference .theta.
between the two signals S.sub.TEST and S.sub.CS'. The compensator
93 integrates the error data S99, and outputs the resulting data to
the counter 90. The counter 90 controls the period T of the phase
count data S90, i.e., the increment value, based upon the error
data S99, and, more specifically, upon the integrated value of the
error data S99.
[0089] The first signal S1 is generated by the calculation unit 96
and the calculation unit 98. The calculation unit 96 generates the
sum of the phase count data S90 and the value "-1800 h" that
corresponds to the target phase value -45.degree., thereby shifting
the phase count data S90. That is to say, the phase is advanced by
45.degree.. The calculation unit 98 compares the output data of the
calculation unit 96 with a predetermined threshold value so as to
convert the output data of the calculation unit 96 into binary
data. Such conversion into binary data is performed such that the
first signal S1 represents the sign of the signal S.sub.TEST'
having a phase that is advanced by 45.degree. with respect to the
test signal TEST. The sign bit of the detection signal S.sub.CS'
may be used as the second signal S2.
[0090] FIGS. 7A through 7C are graphs each showing an operating
waveform for the test signal generating circuit 60 shown in FIG. 6.
The error data S99 changes according to the phase difference
between the two signals S.sub.TEST (S.sub.TEST') and S.sub.CS'.
FIG. 7A shows a case in which the phase difference between the
signal S.sub.TEST and the detection signal S.sub.CS' is smaller
than the target value, FIG. 7B shows a case in which the phase
difference matches the target value, and FIG. 7C shows a case in
which the phase difference is greater than the target value.
[0091] When the phase difference between the test signal
S.sub.TEST' and the detection signal S.sub.CS' matches 90.degree.
as shown in FIG. 7B, i.e., when the phase difference between the
test signal S.sub.TEST and the detection signal S.sub.CS' matches
the target value 45.degree., the error data S99 becomes zero at
each zero-crossing timing of the test signal S.sub.TEST'.
[0092] When the phase difference .theta. is smaller than the target
value 45.degree. as shown in FIG. 7A, the error data S99 is a
negative value. In this case, as clearly understood with reference
to FIG. 5, there is a need to raise the frequency of the test
signal S.sub.TEST. Accordingly, the counter 90 increases the
increment value.
[0093] Conversely, when the phase difference .theta. is greater
than the target value 45.degree. as shown in FIG. 7C, the error
data S99 is a positive value. In this case, as clearly understood
with reference to FIG. 5, there is a need to reduce the frequency
of the test signal S.sub.TEST. Accordingly, the counter 90 reduces
the increment value.
[0094] With the test signal generating circuit 60 shown in FIG. 6,
a feedback operation is performed such that the error data S99
becomes zero, thereby adjusting the frequency .omega..sub.0 such
that the phase difference .theta. become 45.degree..
[0095] Description has been made regarding the present invention
with reference to the embodiments. The above-described embodiment
has been described for exemplary purposes only, and is by no means
intended to be interpreted restrictively. Rather, it can be readily
conceived by those skilled in this art that various modifications
may be made by making various combinations of the aforementioned
components or processes, which are also encompassed in the
technical scope of the present invention. Description will be made
below regarding such modifications.
[0096] Description has been made in the embodiment regarding an
arrangement in which the frequency of the test signal S.sub.TEST is
adjusted such that the phase difference .theta. between the test
signal S.sub.TEST and the detection signal S.sub.CS' becomes
45.degree.. However, the present invention is not restricted to
such an arrangement. Also, other values may be used as the target
value of the phase difference .theta..
[0097] Description has been made in the embodiment regarding an
arrangement configured to drive the fan motor 6. However, the
present invention is not restricted to such an arrangement. Also,
the present invention may be used to drive other kinds of
motors.
[0098] While the preferred embodiments of the present invention
have been described using specific terms, such description is for
illustrative purposes only, and it is to be understood that changes
and variations may be made without departing from the spirit or
scope of the appended claims.
* * * * *